The compliance of the cardiac muscle in diastole is important to normal filling of the heart prior to ejection. In many heart failure patients with normal systolic function, the "stiff heart syndrome" is likely caused by stiffened heart muscle. In the last year we have confirmed the accuracy of a non-invasive, MRI based measurement of heart muscle compliance, demonstrated its feasibility in humans, and showed the stiffening of the muscle following ischemic injury. We now have a protocol to look at patients with hypertension to see if muscle complaince is specifically responsible for their conditions. We also observed a unique feature of blood flow in the heart, the out-of-phase arterial and venous flow in small branches of the coronary tree due to of the squeezing effect of heart contraction. We measuremented tissue volume changes due to this effect, which give an independent estimate of perfusion of the heart wall, and points to a mechanism of very timely coupling of mechanical work and oxygen delivery in the heart.